1. Field of the Invention
This invention relates to remote switching systems utilizing, to achieve the desired switching function, conductive circuits having other primary functions.
2. Description of the Prior Art
Many electrical circuits, such as lighting circuits, utilize the power-carrying conductors to carry control information as well. In these applications it is common to use carrier currents, i.e., currents above the frequency of the power current, to effect switching of the lights or other equipment. Such carrier current systems have the disadvantage of signal loss over long distances, particularly when transformers or other such impedances are interposed.
In other applications, such as in airport lighting, separate and independent control wires are run to remote sites from a control center to effect the switching on or off of lights or other apparatus. Obviously, such independent circuits are expensive to install and may increase maintenance costs because they constitute additional elements in a system and increase the probability of system breakdown.
Mechanical relays activated by line current or a current related to line current have the disadvantage of contact and other mechanical-part wear and produce line voltage drop.
Therefore, it is a general object of this invention to provide a remote switching system which is free of the problems and disadvantages hereinbefore set forth.
It is a more specific object of this invention to provide a remote switching system which utilizes the power conductors as the control conductors.
It is a still further object of this invention to provide a current-level-sensing switching system which is primarily solid state in its nature to assure high reliability.